Ultrahigh-frequency variable impedance element



July 1, 1952 D. R. HAMILTON 2,602,157

ULTRAHIGH-FREQUENCY VARIABLE IMPEDANCE ELEMENT Filed May 5l, 1946 '7 Sheets-Shea?I l ,f c6 G, GZ e l l I I l l I :la

IN'VENTOR DONALD R HA MILTON BY ,1 /w

ATTORNEY July 1, l1952 D. R. HAMILTON ULTEAHIGHFREQUENCY VARIABLE IMPEDANCE ELEMENT 7 Sheets-Sheet 2 Filed May 5l, 1946 f me VTI

INVENTOR DONALDER. HAMILTON BY ATTORN EY D. R. HAMILTON ULTRAHIGH-FREQUENCY VARIABLE IMPEDANCE ELEMENT July 1, 1952 Sheets-Sheet 4 Filed May 5l, 1946 PULS Ez `SOURCE TuNml6` CONTROL MA GNETKGN INVENTOR DONALD R HAM/LTON ATTORNEY July l, 1952 D. R. HAMILTON 2,602,157

ULTRAHIGH-FREQUENCY VARIABLE IMPEDANCE ELEMENT Filed May 3l, 1946 7 Sheets-Sheet 5 VLT GE SOUECE SOURCE I VAE/ABLE VARIABLE VARIABLE VAEIABLE Iva/55 TEMI/NATION /MPEDANCE IMPL-DANCE IMPEDA MCE IMPEnANcE ELEMENT ELEMENT ELEMENT ELEMENT OUTPUT Afa/5E u LEVEL f, f2 f3 f4 f,- f f7 fe F/ZEaI/E/I/cy UTIL 'N DEV/CE.

INVENTOR UNALD HA MILTON wpd/@M ATTORNEY July 1, T1952 D. R. HAMILTON ULTRAHIGH-FREQUENCY VARIABLE MPEDANCE ELEMENT Filed May 3l, 1946 TTORNEY July 1, 1952 D. R. HAMILTON 2,602,157

ULTRAHIGH-FREQUENCY VARIABLE IMPEDANCE ELEMENT Filed May 31, 1946 7 Sheets-Sheet '7 EESONANT FEGUENCy-F- DONALD HAM/L TO/V ATTORNEY Patented July 1, 1S )52 A avere.,

Thepresent inventionrelates to the art including apparatusoperative; in ythe ultra-high irequency'andsuper-high frequency ranges ofthe frequency. spectrumandg; imore particularly, to

velectrically variable' impedance elements having a Wide Variety of uses in these frequency ranges.

,Ilflalthei .ultra-high uand, super-high :frequency f ni 42,602,151

' cULTRAHIGH-FREQUENCY VARIABLE l if, IMPEDANCE ELEMENT o l, onald R. Hamilton, Princeton, N. J., a

he Sperry Gorporation,

ssgnor to f a corporation of Dela- ApplicationMay 31, 1946, Serial No. 673,222 rzci'cialms. (C1. 332-7) of oscillations, an adjustable impedance isoffered to the impressed voltage `Whichnma'y be controlled, both in magnitude and' phase angle or as toV resistive and'reactivecomponents, by the ranges; (for-example.. 'fori frequencies vabo-ve 300 megacycles. per second-.corresponding to Wavelengths, shorter. than one meter) conventional circuit .elements,isuch.jas resistors, inductors, capacitors, and conductors, assume. forms of a highly specialized. nature differing greatly from the corresponding elementsat .lower frequenciesV oruseful Withdirectv current.- The special problemsg incident .to theaV conduction, modification, and radiation of Y.energy oftheseffrequencies requires highly specialized apparatus to perform the norma-1 functions in.- .conjunction therewith, various specialized l .types .i of :which have heretofore been devised. Howevengin-...noneofi .the known' devices is provision .made for .za'fwidely .and readily variablev impedance element capable ,of producing impedance'v values. covering fa .Wide "range ofresistive and reactive components, either pf. these components Y being vpositivefor negative at will, andA readilycontrollablein magnitude Vby electrical potentials. 11;. ,;A ccordinglyit is an gobject of .the presentinvention toprovide a* variable. impedancev elementuseful at ultra-high-andfsuper-high frequenciesand' readily controllable either manually orA electrically .over a .wide -range of impedance valuesp` It is another object ofjthepresent.invention to provide a variable impedance element adapted to serve va wide variety of 'functions at ultra-high and super-high frequencies', such asv a 'variable impedance transformer, Val variable phase shifter, a repeater or amplifier, a variableterminatingimpedance, a variable non-linear impedance, a signal expander, a limiter, an amplitude and/or frequency modulatonga tuning control, a power divider, a noise source, a variable selectivity circuit, a variable frequency circuit, or a variable feedback control, among other.

The present invention makes use of the impedance ,properties of anelectronstream to provde auseful variable impedance element'v servingz; many of they functions, enumerated above. It has been discoveredthat when an electron stream isf passed througha Vpairfofzgricis between which is;imp'r`essed.an alternating" voltage, 'and is thereelften-reflected? to -fbe returned ithrough the. same pair-of grids; ina manner. avoidingithe production adjustment of onevor vmore y parameters associated with the electron stream, namely,fthe 'accelerating voltage producing thel electron strean'r,"`

the magnitude of the stream current, or the refleeting 1voltage-.producingHthe reversal of' the path of theele'ctrons of'- the4 stream. Such impedance .variationsaref-highly useful in a great variety. of systems,L as long the'electron-.discharge -is maintainedin af passive condition in which self-generating oscillationsV are prevented.

The present inventioniprovides several different formsvof electron discharge 'device' useful as such a variable'impedance element and alsoprovides a number of different systems utilizing such a device, either to provide functions corresponding to those provided at 'lbwerfrequencies by conventional devices: or functions ordinarily impossible atsuch lowerJ frequencies... .1 1 l Theinventionin another of its aspects relates .tov novel features ofthe -instrumentalities described hereinfor achieving the principal` objectsof the invention and't'o novel principles employed in4 those. instrumentailities. Whether-or not thesev features andprinCipIesare used for'the said principal objectslor inv the said seld.

A further object of the invention is to provide improved apparatus andrinstrlumentalities embodying novel features and. principles, adapted for use in realizing the above objects and also adapted for use in other fields.

The present invention and other objects thereof will become "clearer upon considerationof the following specification and appended i drawings inwhich:

1 Fig; 1 is a schematic-circuit diagram ofthe impedance element'of the present invention useful in explaining'its operation;' f v Fig. v2 is a schematic :representation-'of the severalelectrodes of the variable impedance element of Fig. 1 showing. their' respective-relative potentials; 2. 'w

Figs. 3, 4', 5 and 6 are various curves andgraphs useful in explaining the theory of operation of the present invention.;l

Fig. 7 is a perspective vieu/,partly incrosssection, of'one practical embodiment ofthe-present invention, useful in conjunction with a Wave guide; 1..; Y' J g Fig. .8 is a'similarfperspective view,` partly-'in cross-section," ofia :modificationY of the 'device' of Fig. 7 j

minating impedance, non-linear impedance', signal expander or signal limiter;

Fig. is a diagram useful in explaining the..

operation of the circuit of Fig. 9.;

Fig. 11 is a schematic circuit diagram. of trie variable impedance element of the present invention used as an amplitude. modulator or adjuster; l l

Fig. 12 is a schematic block diagram of another system using the variable impedance element of the present invention as a tuning control or frequency modulator;

Fig. 13 is a similar schematic block diagram of a. modiiication ofgFig. 112;-

Fig. 13A is ja similar-circuit diagram of a further modification of Figs. Y12 and 13 useful with a pulsed.` oscillation generator;r

Figs. 1I Brand 13C are schematic circuit dia. grams. of systems utilizing the present novel variable impedance-jelementrfor amplitude modulation;` I

Y Fig. 14 isa-.schematic block diagram of. a sys.- tem ,utilizingrthe present noveivariable impedance elementasia power-divider or monitor; Fig. 15;.is.- a-=schematic circuit .diagramofa system. utilizinggthef present. novel variable impedance :element as av lobe-switchingarrange-- ment for.v radio navigation;

Fig. 16 is a schematic black.'y diagram ofasystem utilizing4 the present. no vel. variable impedance; element as a noise source in the ultra-high and vsuper-high Afrequency range;

...Fig 17 isv a .graph ,useful-in explainingfthe'op-- eration oftthe .device eilig. 1.6;v

Fig. 18 is a schematicfcircuit.diagram of a modication of. any ofthe. preceding figures;

fMFig. 19 is. -a perspective view, partly in .crossy section. of a,. r 11odication of 'the devices of Figs. 7,. 8`and 8A, and. useful with coaxialline systems;

Figs. 20j and 2-1 are velevation -viewsypartly in cross-section, of .a further modification.V of. the devices of Figs. 7, .8; 8A and 19 .incorporating a cavityresonator;

Figs. 22+25 .are curves useful in explaining the operation. of; the Vdevices of 2A and 21';

. VFigy26 is. an equivalentschematic'circuit dia,- gram for the apparatusof; Figs. 20 and 2l;

Figs. 217-29Y arecurvesi and ygraphs useful in explaining the operation of the devices of Figs. 20and21; i

Fig. 30 is a schematic circuit diagram of a. system utilizing the present novel variable impedance element as a feedback control.

In the following figures, like structures are given the same reference numerals.

Fig. 1 shows. diagrammatically the circuit for an electron discharge device having variable iin--A pedance propertiesl and useful. as will be seen, as a variable impedance. element at ultra-high frequencies. Thisv device comprises, an. electron.- emissive cathode K, a control gridCG, a. pair of velocity-modulating gridsv G1 and, G2, and a reector electrode R, all in alignment with one another.

Grids Gi and G2 have an oscillating voltage. e=E sin at impressed therebetween, of .radian frequency a. However, these grids. G1. G2 are. usually maintained at the same unidirectional potential E0 with respect to cathode K, as by means of their connection to the same adjustable electron-bcam-accelerating source 29. through respective radio frequency choke coils I8, I9 which prevent a high frequency shortcircuit between these grids G1, G2. Control grid CGis-maintained at an:- adjustable negative or positivepotentiallicr relative'tofcathode K by means of adjustable voltage source 32. Reector R. is similarly maintained at an adjustable unidirectional-,negative or positive potential ER relative-togrids Gi, G2 by its connection to cathode vK rthrough adjustable voltage source 3|.

YGen'er'allyf, both control grid CG and reector Rare-maintained"slightly negative relative to cathode K, although under certain conditions Y either may ybe...positive relative to cathode K.

Fig, 2 shows schematically the various electrodes and their relative potentials. Cathode K, grid G1, and accelerating voltage source 29 serve as an electronfgunzt'o project a `unhierin-velocity constant-intensity electrontstream Sthroughgrids G1 and G2 toward. reflector R. -Themagnitude I0;l ofv this electron'V stream/fis. adjustable byv adj-ust.-l ing thecontrol .gridpotential1.EG,/.as by! varying voltagesource 32.

This constant-intensty. .tand "uniform-velocity electron stream iis `subjected to. Vthe oscillating electric .field .produced by Athe.r'alternati'ng voltage e=E. sin wt ,betweenig-ridsfGi yand; G2. Volt-v age e. vmay be impressed'-betweengrids Gli-and G2 in any suitable manner.. the direct `connection to source SEshcWnJin Fig. 1 'being merelyffaschematic. illustration oflfone way :of producing this' voltages between 4grids.'.Grifand Ge. The oscillating electriciieldiin thev gap between these grids G1 and G2.alternatelyraccelerates'and Idecelerates. .the electrons. r or 'thev stream.. Thus, electrons; passing through. the-fgapfbetween lgrids.- G1y and :G2 .during` the alternate :half-cycles or voltage e :whenA G21 isilpositive'.' relative Lto-Gi will be. :acceleratedry while those Lpassin'g through -the gap .in :the fother half-.cyclesfwill- :be decelerated; This. actionLis termed velocity-modulationofthe electrons ofthe stream;

vThe y'velocity-modulated lelectrons itl-iuspreduced are subjectedvto the lretarding'andl'reiiecting unidirectional electric field betweerr lgrid andireectorR, produced `by the voltage Ea-impressedlbetween these electrodes R-andGr. This eld causes the electronsadeceleratedlin'theigriti gap toireturn Vtothe gapimore' quickly-Strien 'the electrons. accelerated in'llthe Igan a insult, the electrons group together, and the reflected' electron stream which ire-enterslthe--igridv gap through grid Gewilllhavea high frequencycurrent component .i ofith'eirequencyf .w 'vchich: is given-by the-expression Y i4=2IoJ11(r) 'siV TMt- 219i :nimmt-ci.' TCD Where l .Y n

f=2afi r i Here 1 rume/Ei* L tai Where. .1N is `the. `punching time: :of Athe :averagevelocity electron. twhichpassesxlthrough. fthe grid gap at. the instant 12:0,A fand hence neither accelerated-incr deceleratedhin the: rel flector `eld'Y space; lbetween; :R #and G2, measured number fof .cycles of"v .thaimeiquericy.y w. A1so\,.:m is Vthe. beam icouplingxccemcient: indicatmgtrthe: eiectiveness. of--=interactiom .of atheelectransiwith 7 where 1c is a constant determined by the speci ing between R and Gz, It usually much more convenient to vary p (orDN-)fby adjusting ER than by varying E0, since 'em'ain -energy :source j2ST. Also, a' vwider' variation in* it 'produced *in frei-f' sponse to a smaller change in voltage. Variation of` j Varies ltbband4 Xb differently since it varies the Jehaseang-lef.- Yofthe impedance Zb. Fig. 4 shows thev variation of conductance Gb and susceptance Bbgwith for constant E. In the regions where Gb'isnegative, the stream acts the res-ione.; Where ,Gbl S-.b-PQSVe the 219mm stream acts' as f a'floassilve.` .loadv In. the y.region Where Gb is negative, the stream acts as anamplier. Where conductance YGb is zero, shunt resistance Rb .is infinite-,.4 andi the stream acts as a pure reactance. Where susceptance Bb is zero, the shunt reactanceg Xbfisfinfinite and the stantially at lthe center Yof respective conducting roi stream acts as a pure,resistance. For other values A ofigs, the stream acts asaeomp1ex impedance Zb or admittance Yb. These values of Rb, Xb and Zb (or Gb, Bb and Yb) are perodierin and :repeat for every change 4of :21pm 4. Hence, a complete rangeofvaria-tion in these vial-ues is obtained for a variation of over 21'r, which forms the useful range of variationl of 'Ihe variation of Zb with qa and Io (E assumed. iXedl-.maw also 'be illustrated sby EligV 5,; a. plot ofL Xb I.versus Rui forrdlerent values of It and :41,: forffslznall.si'.lnals.` Hence each; point of the plot frepresentsa value ofy Zb.y Curved is. a. circle withcenterf'atfthej origin, :and: represents all values of Zb obtainablefor a givenfxed 1b. As p varies trom .zero to 2r, Zb 'variesl from.- `Zb-counterclockwise. completelyv around Acircle fw. Curve b is a similar locus for av diierent value of Io.

Hence, Io determinesftheradius of the circle, and gf determines the polni-J of the circle which represents' Zbl. also-'shows that; the .limit on; the impedance val-uesJ obtainable. is. yonly the maximum current-'wl'ii'clfr can fbe' usedf. r @Noms r-#Ifthe variationfof -N -is'f considered, these-circles; a,..'amii=b become spirals'li. f

Variationfinr 'alsoaEectsLRb ancLXb. As-.stated above, r=1rNmEf/Eo-. Ot these terms, N and .1m change but-little' andkmaybe considered'constant. Therefore, fthe maj-or variation .is determined by E/Eb. For a given En, r is proportional; tofsE. Fig. 6 shows how Eber-Xb varie'sfwithvrycos-r pibeing assumedconstantand' positive. curve shows that the polarity/of' Rbiand ,.Xbfw-illr alter-f nate, changingeachftime a :zeroo fthe :func-1 tionJ-1(r)-is'passed.` v`l'ig. 'fval'solgrapl-iicalliy illus# strates that Zb ist-fa' non-linear impedance since Rby andA vXb "change radically and ."nonelinearlfy with'tliel/oltage'.-l

However, fior smallfvalues 'o-fr-l (say, less'. thanl, Rb and Xb are linear; `being-substantially:'firidependent of r or E. This is shown* tothe-'leitet ordinated in'1i'g.26.-`V

Thefdevice ffoi fFi'g. 11 "therefore provideszan impedance 'element which: readily '.adjustedffin response tof. electrical*signalsy applied 1to1 reilector Rf', eontrollgridlCGorcathode fK, tol have afwde range-Loresist'ance. orre'actance, either positive on` negative, -and useful Jinmany Ynitrati-hig'li.''fre-fi quency applications, some of Whi'eliare:fdescribed hereinafter., r v

Fig. :1'7 .showsonef structural form Vwhich the variable impedance .device of the present invention may take, especially-...adapted to cooperate with a metallic hollow-pipe wave guide, although plate members 4l audit?. Interposed between the plate members 4l ,and 4.2 and sealed theretol by Aka vacuum' seal"v is arr insulating cylinder"24,3',v suoli' as' ofglass which vforms part of the vacuum envelope enclosing fthe electron stream 'and also serves .to space the :grids G1 and- 'Gjz the. proper.

.distanceE apart;L Arrinsulating end; bel1f44" is sealedtof tiefther' side of `plate- 'merriber '4Z 'and supports'ft'liq reflector R centrally thereof' means of ther j :lead 46'. Cathode K'.v control grid' 'CG and "the eater H kfor thercathod'e. Klare supportedgi'nconventional' vfashion. 'from a 'tube base 4*If wl `1fichisjsealed to the llower s'rde ofpl'ate 41j toj complete the' vacuum envelopefor the 'el'e'cf tronj'di'scl-rarge*path. L A,

' 'late -rr'ien'rbiers;AItIA {and *littl are 'adapted 'toA co- Y "opposite 4walls ot-a 'rectangular ,thisrg'i'1rlgoseA the opposite walls of the "wave :guide are provided vwith ref.. spective fapertnesjfl'' and '49. Preferably aperturej48 is s lightly'la'rger' than 'aperture 4H.. Simi,

larly.v plate member 4| "ismade larger than. plate member ,l 42, *andeach of these "plate, members isadapted t'o 'lit snuglylwithinthe respectivegwave. guide apertures yligand". V49j so that. the plate members 4I and 42 'and grids G1 and 'G'z substantially form continuations `of the wave guide walls. To make good4 contact between the .plate members '4l`42 and. the opposite walls of the wave. guide"%45 .these...p1atemembers may bev 'prQvidedwtIi oiset. flexible .rings 5I. andy 52; 'I' having spring .ng-ers contacting the. Walls ofethe.-

wave. guides, .Accoi-"dingly,F the `variable imv pedance element device. Zbmay be. inserted-into. theopeningsla, 49,.of. .wave guide. 4,5.,y being. held therein by any suitable socket or holdingdevice (not shown.. I, Grids Gr and Gb therein.t effectively form zportions. ot ,the opposite-walls'of Vthe were e l; 4. lt-.arme cette thereof.

ySince ak vubstantialalternating :voltage exists hetweenthefcenters of. these Aopposed waveguide walls duringthe normalqtransmission of higlr frequency ,energydown waveguide '45 this. voltage .be impressed. between :grids G1 and. Gm, and thedevice'. vwillv thena operate fini'the 4manner discussed.above. Itiste be--understood that.` the circuit associated with thefdeviceoilig; -'7. mayvv loe/similar to that v.shown in. Figi. .1'f'or of anyfof theV formsy .shown-hereinbelow;

. -Itywilhalso ybe understoodffthat the. variable impedance.v element may be` permanently .-incorw porated within a. section of 'waveguide ifrsodesired, as by xedly mounting grids G1 and G2 i'napertures in the opposite'walls of such a wave guide f'sectioii.- -and sealmgfthe insulatingmeme' bers 43 and 44 and the tubefbasell'l tothe;Walls` ofthe waveguideinstead. of. tothe :plate members 4l an`d'42.` Th'i's" arrangement sl'iown in Figi 8; Wherethe wave-.guidefsectionfll in' wl'rl'cli' the .device` :2 5 fisintegrallyf' constructed', is as: ,provided .with fcenventibnal choke jointsv 'or couplingiterminalscfor'coupline'tootherisimtlarr'wavefgidefsections.'

In either Fig. 7 or Fig. 8, one of grids Gi .and Gamay-.be put clos'errto the :other .to2 reduce thelgaptransitstimerandmcreasema. Thisiwoul'df. require connecting.-.thatz` one. grid tto` the. wave guide wall by a cylindrical pole piece, as shown inFig.8A. j

The apparatus 'shown in Figs. 7. 8 or 8A is capable of a Wide variety of uses wherever a variable impedanceelementislfdesired `in ultratimes shortcompared to a quarter-,cycle of the,y operating frequency i, such as are usually en countered, 'and will be considered to have that Value hereinafter.` 11(1) istheBessel function ofthe first kindand rst order, with argument r. 1p is the ,phase between the current i andthe Yvoltage' e, taken as zero when the instantaneous maximum of voltage e acrossthe gap occurs simultaneously with the instantaneous maximum olthe radioirequen'cy component of the' reflected electron]y cu'rrn through, the gaio, withlth'e" voltagehaVihga'sense or polarity to accelerate the reflected electrons..` ln thissituationthe re ilecte'd electron stream absbrbsmaxinumenergy from the ioscillating:` "field" in' the' gap between grdstGland flhephas'e 5p 'and the bunching time `N are', of course; related. When 'e' 'is aero, N Vequals "some integer plus`1/4." Ji general, i

if .fetirN Where N -isnot necessarily anintegre. The meaningfulv rangeof variationof eis from 1r t'o-i-jvl-, since -inthi's range cos e assumes allits possible values.V -Nis usually fairly large, as of theordenof-. For V-1r 11 1i, Nonlylvariesby an amount 1,- ksothatior most purposes N can be consideredpas a relatively constant parameterin Whatfollows; 5 '1 Y' -For small-gap transit times (where m='l) the iirst passage of# the electrons* of Athe stream through the gap will, on the average; extract substantially'no -energyY from the -Y gap Yfield. Thus, whenthe-iield accelerates electronaworkis done by theeld on fthe electrons; :When the field' decelerates electrons', the Y electrons do rwork on the field. Since'as many Velectrons are deceleratedV as! are vaccelerated, and in equall amounts, v on the average there .is-'no energy exchange between theiield and thefelectrons;

As to the' reflected stream,r howeverya`I diierent situation exists. Now-there `is interaction between .the alternating electron current componentiand the alternating iield, andthe exchange ofpo'werisgivenby 1- f t .'-glB-Vl/giem A (3) where. the 4bar over .the right memberl indicates altimeaverage. Hence. l.

When =`0,maximum Apower is absorbed by the electron :stream .from the field,r and hence from source' which produces .the iield. -Forother values of 4, less power is .takenfrom the lfield. For cos qa negative, power isr even given tothe field.;y 'f

,The 'entiredevice acts as a variable impedance element: connected acrossnthesource 36 Whe-e I.

and is the D. C. beani' impedance.

This variable impedance Zu may be considered to bevformed by a parallel-connected resistor and reactor, fof vresistance Rb vand reactance Xb', givenby...

cosoA B., sint (9) GOS gb as above.

In this last expression (l0) for P,.it will be seen that In, E and mare always positive. Jur) is also positive for r less than .3.83.. Since N and m are substantiallyV constant, the value of 1' (and hence of J1(r)) is determined mainly by E/Eo, which is usually less than'0.5.

However, qs may vary from -vr to +r, so cos fp may be negative or positive. For

that

-2 2V e cos p is positive, and-the electron streamacts as a passive load, absorbing energy from the source 36, this energy being dissipated in the eiective beam resistancer Rb. For negative values of cos o, power is delivered from the electron stream to the field. Hence, the; apparatus operates as an amplifier, the energy of the Voltage source 29 being transferred to the Aoscillating electric iield in the gap. The resistance Rt is negative under these conditions. l

From this discussion and from Equations 6 and 7, it is clear that the valueof the equivalent resistance Rb vand reactance Xb of the present device 25 is determined by E, I0, and r. The value of E: is generally determined by system conditions, and is ordinarily. not available for adjustment forthe purpose of varying or controlling Rb and Xb. In may be readily controlled by adjusting EG. Such adjustment varies the absolute value `of Zb, and hence varies Rs and Xb equally and similarly. f

The phase angle 4 is most readily varied by varying ER. Even a relatively small change in ER can vary gb through a range of 21r (or 3609). can also be varied by varying Eu. The dependence of qa Vupon Eo and ER is illustrated in Fig. 3, which shows a series of curves in which ER is plotted against Ea. each curve having constant qs (and hence constant N).

Analytically, it can be shown that, for a .plane parallel reflector, and ignoring space charge,

high-frequency systems. l portant of these uses arej'described hereinbelow with respect the following gures. i

Referring to Fig. 9, the variable impedance device 2-5. of the construction shown in Figs.

`Some of the more im- 7, 8 or 8A is indicated'schematically as incors porated in a wave guide 45, 45' extending be-y and easy method `of accomplishby serving as an impedance transformer between the 1oadj31"and `the'wave guide 45 so as to ,match the impedance ofthe load to that of the Wave guide. above with respect toFig. ,G ,jthe variable impedance device 25 may be adjusted to have device 25 ofthe present invention s As indicated substantially any desired impedance lvalue, by adjustment of the reflector voltagefllal and the beam current It, as by' means 'of the` adjustable voltage sources 3| and' 32,' respectivelvL Theresistive component Rt and V reactancey component Xb of this impedance value may be independently adj usted to have desired values. In addition', both the resistance and reactance' components or either of them may bemade `either positive o'r' negative, as desired. Accordingly,

would ordinarily produce' standing waves, .the device may be adjusted, by?V adjusting voltage sources 3 I and 32, to modify theimpedance value viewed rightward in Fig. 9 from vthe position of device 25, to be substantiallyeq'ual to the characteristic impedance of the wave guide 45.V By so doing, standing waves with their concomitant .disadif thefimpedanc'e value of V the load 31 asseen from the Wave guide,'45 'pro-l vides a mismatched impedance condition, which vantages are substantially eliminated fromthe wave guide connected tosource 36.Y

As an exampleof how such impedance formation may be obtained,` reference is" made to Fig. 10, showing an admittancediagramin which the horizontal axis represents`v conductance Gb e and the vertical axis represents fsusceptance Bb. The point YQ indicatesthe characteristic admittance of the waveguide section 45 .to .the source 36, whichis assumed-the same as thatof the wave guide section 45'k connected to the load 431. Also shown in Fig. 10 area series o f circles C1, C2, C3 which form the well-known bipolarcoordinate system having Y0 and -Yo as the poles, thereof.

It is a property of wave guides as Well as of two-conductor transmission lines that, if fa load of admittance Y1 is` coupled to, one end of a wave guide or line of lcharacteristic admittar'iceYty then the admittance as' viewed from-points of said wave guide spaced from the load by differing distances will be represented bypoints on the loi-' which vthe admitpolar coordinate vrcirclef upon tance Ylis located..l This is shown circleiCi in Fig. 10.V Accordingly, if the load 31 lis assumed to have an arbitrary admittancevalue such Aas Y1, then when .viewed from the Alocation lof the transimpedance element 25, thel admittance of the load 31 and its connected .wave guide45 willfappear I to have an admittance value such as "Yz, also located kon circle C1.' Ordinarily, thesection'of wave guide 45' will'be made relatively'short. vlin order to march' the mais 31 te thewsveguide 4 5;

itis necessaryithat this admittancer Y2' be trans- A formed to the value Yu'which is thecharacteristic admittance of the guide 45. For this purpose,

it is necessary to add to the admittance Y2 van admittance shown by the vector Y2Yo in Fig. 10, and also plotted from-the origin of Fig. 10as the vector OP'.

It will be seen that this vector OP has a negativeconductance OQ and a negative susceptance OS. Accordingly, the Voltage ysources 3l and 32 are adjusted in accordance with the considerations discussed abo-ve to cause device 25 to produce a negative conductance of amount O Q and a negative susceptance of amount OS. rIhis negative conductance and susceptance are in shunt with the admittance Y2 and therefore are added directly thereto. Accordingly, in this manner, the variable impedance device 25 transforms the admittance Y2 tothe admittance value'Yo, as is desired. It will be appreciatedthat'for other values of admittance of the load 31, other adjustments of the variable impedance device 25 may j rbe similarly made so as to provide proper matching or impedance transformation as desired.

The system of 'Fig'. 9 may also be used as a phase shifter lor lineV stretcher. As is well known, the bipolar coordinate circles, such as C1, C2 of Fig. 10, form ythe loci'of constant standing Wave ratio; that is, if a circuit elementof variable admittance is connected tothe end of 4awave guide or transrnissior'rv line` of characteristicadmittance Y0,the standing wave. ratiol existingv in that guide or line will remain constant despite variation in the admittancerofthe circuit ele-' ment, provided that the various admittance.` values of the circuit elementare lpoints of a singlei one rof the bipolar coordinate circles showninY t ured by the arc Y1Y2 of the circle C1..

The phase of the wave arriving at the load 31 v maybe altered by lchangingthe `length of the waveguide section 45. `However, this is awkward and inexpedient to do. mechanically,since it is of practical importance in wave guide systems to keep theV elements in Afixed mechanical relationship. The present invention, however, provides apparatus for producing suclra phase.. shift of anamount which maybe readilyand even electronically controlled. l..

As discussed above, a change in the phase shift merely means (and is accompanied by)` .a change in the admittance valueseen from'the position of: the `device 25 to a different-value onthe-same' coordinate circle (such as C1), r Accordingly, additional-phase :shift .may be interposedr by transforming the admittance value Y2,;;viewed rightward from the right of device 25, to another value, such as'Y3,.-v separated from Y'falongthe' circleCi by an arc corresponding*tothe'desired l phase shift. i In the-present instance, this may be' uoneby adjusting'the ericuit parameters-'off the variable impedance devicei "to cause it to assume an effective admittance given by the'vec- "f tor Y2, YB. 1n this way-'the admittance senrqn'r j the end ofwave guide 45, viewed rightward in Fig. 9, will have the neW'value `Yajand the'effec t upon lthe load 31 in fthef'same'. .as ;thoughfthezi;

length of the wave guide'section 45' had been 13 modulating signals and thereby produce aA correspondingly varying impedance across the wave guides 45, 45', so that sults. Alternatively, the modulating source shown at 53' may be connected vinseries with the control grid ,voltage source 32 to vary the control grid voltage by the modulating signals for producing modulation of the ultra-high-A frequency energy from source 36y by the modulating signals. Also, modulation vmay beproduced by use ofthe modulating signal source 53fr connected in series with the voltage source 29V to vary the beam voltage Eo by the modulating signals. The modulating signal sources 53, 53', and 53" may be used singly or in combination, according as diierent modulating characteristics are deamplitude modulation re'- signal sired. It is preferred to use the modulating sig: Y

nal source 53, since here a lower amplitude ci modulating signal and lower power output from the modulating signal source is required to pro-` duce a given intensity of modulation.

The variable impedance device of the vpresent invention is also useful as a tuning control, as illustrated in the block diagram Fig', 12. In thisA figure there is schematically illustrated an ultrahigh-frequency oscillator 54 having a cavityresonator as the tank circuit or frequency-determining element thereof. Coupled to the resonatorA by a suitable high frequency energy conductori, preferably of the wave guideV orcoaxial linetype, is the variable impedance device 25,y similar to those shown in Figs. '7,8 or 8A. Also coupled to the variable impedancedevice byy a.v furtherY quency modulating the output of an oscillator, it

is mainly the variable reactance qualities of the variable impedance device which are used. Ac-

cordingly, a highly useful operating condition is -that for which the resistance Rb is infinite or conductance Gb is zero. For this condition, c is adjusted to make thereactance a maximum. and the Q of the resonator to which the'device' 25 is coupled is not lowered. The magnitudefofv the reactance is then readily adjustable lby varying The polarity ofthe reactancec'an EG to vary lo.A u o l bereversed'by altering c byyl80, as by resetting the value of ER. Ordinarily, in this type of oper- A' ,ation it is most desirable to have asmall ratio of This method of tuning or modulating is especially advantageous in those vultra-high-'frequency oscillators where it is ordinarily impra'cticable to vary the resonant frequency of the Vresonator by mechanicaldistortion or alteration 'ofthe-shape of the resonator.l Magnetron: oscillators l'of all types form one class of such oscillatorsfor which the present invention has" especially high utility.

conductor 55' is a suitable non-reflecting ter-` minating impedance 51 of any conventional type n adapted to absorb all high frequency energy incident thereon so that no reilections or standing waves are produced. This terminating imped-V ance may be another variableimpedance element according to the present invention, as described above. As discussed above in the generaldiscussion of the characteristics of my `variable impedance device, this device 25 may be adjusted to have widely varying pure reactance, either negative or positive in character; thatis, either in-v ductive or. capacitive reactance.' When such a reactive impedance is coupled'to-:a resonator, such as that of oscillator 54, archange-fin the resonant frequency of that resonator occurs. Y`

Such change in resonant frequency ,necessarily produces a change in the output frequency ofthe oscillator. The reactance of the variable impedance element 25 is readily adjusted under the control of the variable voltage sources 3| and'32 connected to variable impedance device 25 as shown in prior gures.

paratus produces a readily adjustable' oscillator Y frequency which is variable over a widezrange and can be adjusted manually bymanually adjusting the impedance-controlling'voltages EG, Eo, and En, or automatically'by` controlling any one or more of the voltages by signals `,derived inresponse to the frequency condition of-oscillator 54, in any conventionalfjmannerflnown in the.

automatic frequency control art.

Frequency modulation ofthe output of they oscillator 54 can also bereadily produced by oonnecting a modulating signal source shown at'58 in the circuit of the variable impedance device 25 in any of the ways illustrated in Fig. 11.

In each ofFigs. 12 and 13, where the variatie` impedance element 25 is used for tuning orl frel u .Y If desired, the non-reflecting termination 5l In many types of radar'systems, such `magnew`l tron devices arer used to generate periodicv high intensity pulses of radiation. f Such a system is illustrated in Fig. 13A where the magnetron'oscillator54 is'controlled by the lpulser |50. TheI Value of bunchingpara'n'ieterI 1' ata useful value,

the beam voltage En of the variable'impedanceY device is pulsed in synchronism withvjthe magnei tron pulsing. Thus, the puiser |50 has its output supplied to unadjustable :voltage divider |60, whose output in turn is connectedin series with cathode K andthe beam voltage Vsource 2,9. `In 'Y this Way,'the beam voltage is maintained small for small or zero magnetron output, but isgreatly increased as the magnetron output (and consequently E) is pulsed on. In this way, r can be maintained constant despite variation'inrE. e Tuning is accomplished by varying the reflector voltage source* 3| or the' beam voltage source 29.

Modulation may be effected by connecting modu-` lating signals in series withfreflector R or cathode K. Control grid `CG may be used, if desired, in the manner vdescribed hereinabove. i

Thepresent `method of tuning or modulating is especially advantageous when usedwith velocity modulation or klystrondevices.- Fig.'l3B

showsY how this method yis applied to a cascade amplifier klystron |2|,' such as of the 2K35 type,

shown schematically in this figure. n Ink such a klystron amplifier, the input signal from a source |22 is' coupled to an input resonator`|23. A second resonator |24 servesv to amplify the signal,

and an output is derived lfrom Aa thirdor outputy resonator |25 andis'sup'plied to a ,suitable load, such as radiatorV |23. An electron beam is oprojected successively through thethree resonators to provide amplication. l

' In such an amplifier",A outputarnplitude is a function of the resonantl frequency ofthe second resonatorl24. iAccording toA the present invention, the variable 'impedance element 251sy coupled to this second resonator |24." Thus,4 by adjusting th'e potentialslapplied to impedance 'element 25, lor by` varying these potentials in accordance with modulatnig signals, the output from Ythe amplifier l2 y is correspondingly adjusted or amplitud'e-rifiodulated.`

However, whenfthe res nantfreduencyfof the 'amplifier resonator is varied, the"re1ative` phase 15.?,` of athesescillatiena-aavithixrpthel` resonator ...to the,... resonantzfrequencyf.. component of .the-hunched f electron"sheamscuintent.` is varied,.resultin'g.in 1a slight,.amount '..of'fphase modulationsin .addition to I.the;amplitude .n1odulation To Tobtain...absoel ,5 lutely. puresamplitudemodulation, .theresona-nt,... frequencyeofsthe ampliiernresonatmnis left .unchangedzrbutqits :Q fis variedfin `accordance...with thefncontrol. -or modulating signal,-. by controlling the .variable-impedance device.. by that signaland 1.0 producingfafresultant.impedancevaluewhich re-` ilects.iinte-.the .ampliiie .resonatorl .as .a pure..re sistance;..fo11owng; the theoretical consideration discussed above..-.1t.will be...understood .that if the output cavity resonator of an amplifier is .15 detuned..i sthe1amplitude `of. response. goes ..down; but; the relativephaseof the hunched beam .cure r rent sandgthe-output resonator. voltage .is also,... changed, so v,that:thecamplitude modulation -prof ducedfbys.varying.:the-resonant..frequency of vthe .20.,

output, `A`resonator-cis accompanied. .by a type of phasetmodulationm However,y if the resonantfre-.- quen'cyg is kept .AnXediJandT-.only-iheiQ is changed, pure` amplitude modulation; is obtained unaccompanied byaphase orfrequencymodulation.- 25

Another swayfto .obtain pure. amplitude modu y lationforadjlustment is illustratedfschematically in iFig. 5130,. .whichfshows r`an.. oscillator-buffer. klystron. I21,:such.asof the..2K34.type.Such klystrons ualso include. three `resonators .I 28,`. I29,- '30 I3ILA :the lrstwtWo'` being coupledl by ,a feedback connection` .I3 I and forminglan.oscillator-.section.. The. -last,-resonator 30` :is an foutput or buffer resonator; Acoupledcto theloadj 26e. :Output -reso-,. natoraI30.-;is. thus onlyrelectronically coupled .to 35 the:A :oscillator section, andaits loading. does n not.. aiecrfnthe,.outputfrequency;Y vHoweveigthe outputlampl-itude. depends on-.thetuning of resonator I30,f.which-imayf be varied; or` modulated .bytheA variablesi-mpedance. element-.25 .coupledithereto 40 Again-ypureamplitude adjustment or modulation is producedfby adjusting the potentials applied to impedance@4 e1ement.-25 l`or :by varying. .these potentia-lsrby' modulating signals.

A further use.of-thevariable .impedance ele.- .45 mentfof` the :presenti-invention is as a` power.di vider'I'his-isfillustrated-in Fig.- 14. As Vdiscussed i rela-tivefto Figs. 9. andilflfthe variable. impedance element 25, when-.interposed between asource 3.6 i and. `a loadfor utilization .device.,such as .31, .can serve to control-the..power...ilow=between-the source and the .:load.by vvarying.theimpedance match,betweenf-source and.- load. .In Fig..` 14 .a single;seurce v36 feedss two separate .loads 31 and. 3'I:.'.A Interposedfhetween the .source ,35 Vand each .55 of Ythe loads :31" ,f 3 1 .is a-respectivevariable. imf pedance elementflfeand2.55'.- of .the.,.typeA dis-- cusseds:.abo/veen;` By-.-.adjustment of the voltages, applied'fto `vthe;respective electrodes of these.im. pedanceeelements25igand 25f!, theamountof 60 power.- delivered .bythe-source f3.6to theloads 31 and-3W can .belindividually controlled.v .For exeY ample, by such adjustments.. xedpercentage of the power output from .source'36 may .be supplied to load/,312 .thememaindergoing to load 31".;V

One applicationpf. this. system of Eig; ldmight be @in monitoringtheipower flow. from .a source 36-to al useful 11oadl3.l.,llin Whichcase the other load-137'!VA might be..aJ wattmetenor other power-. indicating ...device., .The .variable impedance ele- 70 ments 25C and. 25f1fare then. adjusted `so that a smallxedfpercentagepf thejpowerowing from source 36 will ow'to the..m onitoring1 evice 31";- thesremainder ilowing tp the luseful" 1oa`d3l;

AsafurthertYDeOf '.systemsimilar tojFig'fli, 75

=,to corresponding-.antenna while the. other` l putin al. condition .completely blockingfsuch. en-f.. ergycow .to .'th..other. antenna. For.Y the. next... halecyclelenergy.,ilows-:to nthe other. antenna, andnot .to thelrst antenna; Inthisywaytheltwo.

. antenna loads .311 ",31 "'would .'bealternately .en-.-

ergized,,.producingalternate .overlapping radiant. energy; beams .whichmay serveV to vdene .a course for'guidace of aircraft orotheivesselsby their interactionlor equieintensity. axis. i 'A This is illustlatedf'in'lig."15;' wherein two die rective antennaeilgand 62f1are shown having slightly .overlapping',A highly' .directive,. radiation patterns.: These antennaeare illustrated as be'- ingjelectromagnetic horns,` but. any` other types f .of antennamaybe used; Each of .these antennae 6I., `Ii2Y fedby a respective ultraehigh-frequency. conductor 153,"6v4fin which are incorporated respective variable impedance elements .25` and .25T 'i` similar :to `l'those discussed above.; The .conduc-"i fre'quency-conductorl 'andthereby to .a source 68 -of ultraehighffrequency"energy to be radiated.` i fromthe-'ante'nnae '6^I1and'62. ":The `energyjis val-r' ternately .emitted from L the respective i antennae 6I and 62 'underthecontrolpf a switching-voltagev source 69,'-"Whiclr preferablyy produces-a squares wave output. VvAssho'wnby Way of illustration'in. Fig.' 15, this switching-voltagersource 69 "is coupled'tin oppositephase 'to theI respective control grids-of the impedance elements25ftand 25"""and` thereby serves 'to jva-lternately Y 'bloclr andunlockI theconduc'tors 'I3a`nd 6Min oppositephase so as to alternate the-ienergization of the antennae 6 I and 62.1# f i If 1desiredftheradiation from feach' of the two loverla'pping-pattern antennae 6I,^`62 canbe sepa-v ratelyiden-tid bylimpressing separate modulating signals threonfThsysten'i'of Fig. V15 readily* and conveniently rpermits'"'suchv additional mod-A ulation.q 'Ihsfasshown in this figure, separate# 'modulatinglso'urces.59,li6g'lof respective modulate ingfreduenciesfi, z, mayfbe connected lin 'series Witlr'fthe frespective'adjustablereilector voltagel source'sof impedance; elements'25'; 25'.v so as to 'I modulate the"energies transmitted along Vconductors 63;"f64 andi-radiatedtfrom antennaefl,vv i

62 -by these #respective modulating 'frequencies f1 y and# f2, iandfthereby Htc identify? `the.*respectiveradiated rb'eams. In thisway' separate, alternate; 'f overlapping and fseparatelyidentiable radiation patterns-areproducedfwhich are highly useful in the fradiolf'guidanee'of vehicles. By the use-of sine wa'veoutput "fro'nlfsource 56S, Vthe antenna radiationfipattern can-bes'moothly'V scanned vbe- 5 tween two :extremepositior'isr` Y As a stili further-application of thenovei-variable'i impedance element of the present Yinvention;y it maybe"*uti1izd ias ani extremely Vwideband'noisevoltagesource.'1 This is illustrated in Figi-'16." Incalibrati11g'-receivers `of ultra-high.: frequencies" an'f important" characteristic. deter.- mining the -usefulness -andL efciency of such .receivers' is the lowest 'signal' level" whichv can' be received in comparisonto thefnoise level. Ac.-V

vcordinglm .standardnoisefsources arerequired for 17 measuring such signalfleyel. any electrondischargeampliiierdevice, noise voltages; areproduced, due in large measure A,to the so-called shotr-seffect. input-*signal isapplied to the amplier device, the noise -voltagesf i being-l of l relatively. low i amplitude compared to the useful signal, are .negligible. However,l Whenno'input signal vis, fed .to an amplifier oflhigh amplification factor, substantial noise voltage is produced. Inthe noise sources in fgeneralvuseafor ultra-high frequencies, only agrelativelyl narrow band lofffrequencies oi noise; can be produced in View ofthe. fact that -rallsucli known ynoise/-sources utilize resonant circuits which necessarily limitthe ,band-width* offlnoise .evoltagesxlproduced. The present invention-:provides a'fhehly; .useful noise-source which?hasT a frefluency .spectrum or band-widmet. @markedly higher;order1ofmagnitude than those previously ikn'own. YFlor-exan1ple, noise voltages-l in the Lfre- Lquencly range from 300 to y30,000 :megacycles f per second f-(oner-.meter to one centimeter; in--gwavelength) may; be .l simultaneouslyproduced.

:indicated .above inV 1- the; discussionj of `fthe `general characteristics Aof lmy f novel `4impedance element, this impedance., .element has negative lresistance ,(andaccordinglyv serves as an ampli- Tfier) vfor. those tvaluesof; `telforuvwhich cos. fais negative..A Stated-in 'other-words, suchnegative resistance isfprfoduced;forfan-electron transit ltime .N-of'v-aluebetweenp andfp-:l/Z, Where. p is -fany .posi-tive sinteger. y Accordingly, amplified-:noise voltages will be produced by such a deviceinthe ifrequency ranges for which thesparticular elec- .tron-ftransit timeof .the t i device ,corresponds to "the intervalb between .an integral tnurnbert-puof ,cycles of thatfrequencyandp-yel/g.

This. is-schematically illustrated ini-Fig. -l'l-in :whichv noiselevel is -plotted against frequency. .For assparticular transit time T, .thereiwillfbe a frequency fifor .which this transittime is ain-alf- :cycle..-1Frequencyf2 isthe frequency .for-.Which -thissame transit itime T corresponds-to onelfvull @-cycle. @Between frequencies f1 and f2 .thefvariable limpedance element serves as an -amplier andi has Ynegative. resistance. and

r`noise voltages which are distributedrthroughout fthel'frequency-range into fa Theffreqllencyjl islthe lowest ,frequency component, oiA the noise .sgnalspro'duced 'Similarlyfrequency f a ,repre-l sents the frequency at vwhich Jthe givenv .transit time 'I'. correspond-sto -/2.cy cles, andthe `frequency .f4 thatfor .which ,the transit time 'I2 is l.two .'.cycles.. ...Between f3 and f4 noise voltages ,will'be .-p1:odi,iced.v Similarly, f5 and fe aretheilfrequencies l)at...wliich the transit time T correspondsltof E/2. an'd `three, -cycles,. respectively, ,and v,between Awhich morenoise voltages are produced. .'There are similar further ranges of. noi-se frequencies upto .a limiting frequency at-which theeiiiciency .ofthe .devicejfallspi voltages are insignificant. No, diiculty. exists in vproducing suchy noise voltages over at 'least 20 such frequency. ranges, coveringthe.. range .of (300 toj- 12 ,000 megacycles :peresecondsfor example.

theapresent inventionproducesaseries otequally separated Ifrequency spectra in rwhich noise., is

variable; impedance element y.transit tdsuch .an extent that the. noise i -In -ordinary operation, whengan accordingly t .L produces Accordingly; it will he seen that theV devicefnf 5' 65 70 fztimeTi'vsuchLthat f2 `corresponds.tooneahalf cycle noise Lfreliuency -yallues intermediate those .shown inFig.17.

Eig 16 Vslriows a systeniadapted `toproduce such noise signals. flnahis figure.,` the variable pedance elementill ,of thesarne ytyp'eas discussed above-haynefan .lectron transit time' T in the re .est ffreldspassisefves-io.prsdulandse spectruinzfshown `.inligri l'l. .'TheQVariaMe irnh mayjc'e` located closely peldenceelemenfllwel 'adjacent the elem nt .Il [tris provided with a diiferent transittiine 'I ".,..andfac`cordingly producesa requency-spectrunifsimilar to Fig. 17,v but displaced.; withr frespect theretohand .thusV :supplies otnerlfrequencygconi ents Ialcsentfrom,timeoutput. zof theelenient'gll. lillernent AI2 ,alsofservesto arnplifyzserne 'of tli'enoise components' y produced .loy- .element f1 l.' yA nonfreectns.termination 13 rnayllae c eiiple'dftcy he` ther'side of element v1 I lto prevent lstandingw pyreflectiongifsso desired, .al-thougnthis'ermn .t 1,113 Afrnas'fbe.,dtlittf'edl `Furtherv vari-able t i n, e dance elements'rilmvj, ,etc-.1 ay be, ,.Cerisefled`r 11.: the system.' to seri/@ias ,other noise sources or `as.;amplifiers `or repeaters and to increasev the ilevel .eff theV noise signall te va .useful output'ilevel. Atuthesame-time thesev'fu'rther elements lL-15, etc,.`, '.i'njay'be ,adjustedto "cmPQhsnts-io'ihe'noisegsisll- "Ofi the. 'je Oi/edissuesed, applications .0f

*the 'present investiga-such as menige. '1; .thrgugh d nce leinent of `theinvenjI'Zjthevariable u non .sheyn'as 1. cremated-,directly in the Wave siiidethroes'hvhic ultra-hishffrequeny Dover news. 1 Ll-Iwei (er, 7th 4 smlnotan essentialfeondition. Onthe contraryji'n any V'ofthese systeins, the variable impedance element merli@ o'ririec'ted irnslnint'rv with-tireY inain Iwaveguide retlier high frequency 4Vjen rgy Qcic'rrl'iu.tor,l and fstili i `serve equally' well. is 'isiillustrai'fed" in Fig!" 18,' Awhich -shoii/'S @general system-similar to those fof f the eabove"g ures`.f-` *the energyfreinfthe"source j j e i *I enfoncer/resist'througii'the ultralhigh'irequency energy'icnducto'i- 45",- which may 'be "a--fwalye guide or lal ceai'al line vorv afparallelwire "transmission line. The" variable 'im-- pedance elernentgZfi` iseoupled to'tliis mainconfductor 45 'fby 1 afsuitablefconneeti'ng conductor y'39 connected ingshunt` to conductor y(15. The'circuit rovelenient 1-25 grnay be any lof` 'those' descrilded Aabove.: Injthis :ways-any 2 impedance variation of @the variable'impedance?elemet'rZ' is reflected through the conn cti 'g condictorfto a''j;ip`ear in shuntiwitliftheflcoiidiictor2M; and produces a result ssupstafntiallythe [saine as"A though 1`the elejmentf25 were' directly incoporY V'in' "thel lconductor xlll', l in the shown in they ypreczfeding 'fleuves A Iiorlrreeetine termination' 8i. di.' any suitable typehmaybe coupled at thelotner' side of vthei`A element 25 ltef, preyentv the A appearance f of atlthe location ofthe elernent' 1wl'iicli e might disturldthe `'eui'erati'ng'feharacterf astres-ef theelement 25.

Jan+embodi1nent of v.a ivarlo'le A'frequ'ent'zy elernent .pedance element in conductors.

accada? 19 with other high frequency conductors having one grounded terminal.

In this gure, the heater H, cathode K, control grid CG and reector R are the same as in previously described embodiments. The envelope E of the device is is preferably of metal construction conventional in the electron discharge art, the various electrodes being connected to lead-in terminals passing through small insulating seals in the envelope.

The device of Fig. 19 differs from those described in Figs. '1 and 8 in that the grids G1 and G2 forming the gap are replaced'by a pair of diaphragms D1, D2 connected to the inner metallic wall of the envelope E. Diaphragms D1 and D2 are centrally apertured for passage of the electron stream, having either a single opening or a grid-like structure at the centers thereof. Mounted between diaphragms D1, D2 vand insulated therefrom is a cylinder C surrounding the electron beam path. Cylinder C may be provided with grids across its ends, if desired. The diaphragms D1 and D2 together with cylinder C form two gaps, separated by the length of cylinder C. This cylinder C is preferably selected to have a length substantially equal to the distance traversed by the electrons in one-half period of the operating frequency, so that the electrons experience similar action at the two gaps. Cylinder C is connected to two lead-ins 65, 66 passing through insulating seals in the envelope E, and is thereby connected to the inner conductors of respective input and output coaxial lines l|9 and |20, whose outer conductors are connected to the metal envelope E. These lines ||9 and |20 serve the same purpose as wave guides 45 and 45 in Figs. 8 and 9. The apparatus of Fig. 19 may thus be connected in any of the systems described above, and will operate in the same manner as the devices of Fig. 8 or 9.

In the embodiments of the invention and their applications described above, the variable impedance elements of the present invention have been utilized directly in conjunction with ultrahigh-frequency energy conductors of various types and have been shown to provide variable impedance characteristics highly useful in numerous diiTerent ways. However, the present invention is not restricted to the use of the im- The variable impedance element described above may also be used in conjunction with a resonant circuit. preferably of the cavity or hollow resonator type.

This is illustrated in Fig. 20, where an impedance element 25 of essentially the same construction as that shown in Fig. 7 is illustrated in conjunction with a cavity resonator 2|. The cavity resonator 2| is formed of a pair of cylindrical conductive members 16 and 11, respectively engaging the grid-supporting plates 4| and 42 at one end. This engagement is preferably frictional so as to permit replacement of resonator 2| by other resonators of different characteristics where desired. The cylinders 16 and 11 are joined at their other ends by a closure member 18 to complete the enclosure of the resonator space, which is accordingly that space included between cylinders 16 and 11 and between plates 4| and 42.

It will therefore be seen that the resonator 2| is essentially cylindrical in shape but of re-entrant configuration, and having the electron stream from the cathode K projected across the re-entrant portion by way vof narrow gap between the grids G1 and G2. The circuit and voltage sources associated with the impedance element 25 of Fig. 20 are the same as those shown in Fig. 9 or 11.

If desired, the impedance element 25 may be integrally incorporated with the resonator to form a unitary device. This is illustrated in Fig. 21, Where the grid G2 is supported in the end Wall 82 of the resonator 2|. Resonator 2| also has a cylindrical side wall 83 and a flat end Wall 84, in which is mounted a re-entrant inner cylindrical wall 85 supporting the second grid G1. Cathode K, control grid CG and reflector R are aligned with the gap grids G1 and G2 as in the preceding forms of the invention. Reflector R may be supported by an insulating or metallic end bell 86 sealed to the wall 82. If a metallic end bell 86 is employed, means must be provided for insulating the reflector R from grids G1 and G2. Similarly, the cathode K and control grid CG may be supported by a further insulating or metallic end bell 81 sealed to the other resonator end wall 84. If a metallic end bell 86 is employed, means must be provided for insulating the cathode K and control grid CG from the grids G1 andGz. Coupling to the resonator 2 I is effected by a pair of coupling loops 88 and 89 connected to respective coaxial line terminals 98 and 9|. Vacuumtight seals 92 and 93 between the inner and outer conductors of the coaxial terminals 90 and 9| maintain the resonator space vacuum-tight for passage of the electron stream. Similar coaxial line terminals 19 and 88 are provided in the device of Fig. 20.

The devices of Fig. 20 and Fig. 21 are useful in the same manner as discussed above with respect to the impedance element of Figs. 8, 7 and 8A, the major difference being that the impedance value offered by the devices of Figs. 20 and 21 now consists of the combined impedance of the electron stream and of the resonant circuit of the resonator, the electron stream being eiectively connected in parallel with the resonant circuit so that the admittance value of the stream is added directly to the admittance value of the resonator.

This situation permits the combined resonator and impedance element of Figs. 2|) and 21 to be used in exactly the same manner as discussed above, the resonator then being normally tuned to the operating frequency. However, one precaution must be taken, similar to that noted above. If the electron beam conductance Gb provided by the variable impedance element 25 is negative and has a magnitude greater than the conductance of the resonator 2| or 2|' combined with the conductance of any load connected thereto (such as the utilization device 31) selfsustained oscillations will be produced in the resonator 2|, even though source 36 were disconnected. Such oscillations are undesired when using the device as a variable impedance element or in any of the uses enumerated above. Accordngly, in the use of the device of Figs. 20 and 21, the beam conductance, if negative, is always maintained at a magnitude less than that of the impedance of the resonator and load combined. Of course, if the beam conductance is positive, no diiTculty of this type is experienced. This condition is maintained by the proper adjustment of the reflector potential En or the control grid potential EG or by proper selection of the impedance of the load 31 in relation to the other parameters of the system in the manner discussed above. This condition is termed a passive state. since the variable impedance element then can# not oscillate.

"The impedance elements L of Fissi '20 f arid'jZl, using a y cavity resonator; may 'be' used "exactly" as elementsof Figs. 7-19 are'used,

Y., e 'impedance and may 'be substituted therefor in 'any of these plings. Infaddition', it is'useful in other applicatonsv,"de scribed heeinbelow.

A The,v operatonof'the typel of device 'shownin gs .20avr'1 d'2`1 maybe better'understoodrom l `:the: following analysis. 'jjlfsfcoupled to 'the resonatorl 2| throughthe terminal 1 5),v an alternating voltage 'e'vvill appear fbtes/een grids G1 and'Ga. .While the electron beam fro ythe cathode :Kfis not owingias'whenxthe jd e is disconnectedfrom'its'voltage'sources);

povrjdissiated in the resonator 2 Vandits coupled load s1y is given byy s ntorz ly in wshunt with that 'of theioad 31. l

U i'`ulosltit'uting the value of E derived from the v/fielnitiojn of the bunching parameter @the dissi- Vpated power may'be expressed as follows:

It will' Al'tes'een that this parameter @is a ciruit efd'ebedig only upon 'the' circuit' 'confidndiretiiai potentials applied' to' fthe ab l 1fat1'is,"andf independent of the' inputv vo1t`fage `vvv`E. Equation 1v2mthentakesv on the'form sh'aeaapgfvel tiieii'ower tijeivered 'tortue eiston bjeairr, (hoWAas/sumed flowing) from the source 36 may be expressed as follows:

2 -P -g-'JrrJloyaoaQ (16) v'therv characteristics of the rpresent y, v' rived `from'Equation'1.6, 'arefshovvn in Figs. 22 t fmgh`25 These gures'fshowthe urvesgof total*j power Pfdelivered by theV f's'bu'rce ""lciitteld:` againsttlie bnching. parameter r; 2 shows two curvesv for av small value "of A uitfparameter 111,' Acurve'r a being for a" positive alge A c3155 vcos gb; 'vrzhile vcurve bfis" the correspondgfiire's by merely 'using `the proprtype of cou- Assuming 'ithatz source*l vgy curvefornegative value of cos 11. Fig. 23, rlysyhows curves c and d 'fo'rvajlargevalue" here R. sltheeiective impedance of 'the reso? that impeda' *Y* `jiandtherefore serves 'fas an cs cil Uwhichis Y, t s the-"present fiveritioii. #It is j to 1 .fromfs'ourc TF0 they.. e

voltage gfier than their@ j'stinatidnsmaybeistopped,Erri va also be increased:'abovelza!V vsofav to fthms,V by increasing y N; iasbyr dec proxirnately 11:7.025

' is :anni 2 5, l 1:51 hetween' Athe .vaiaesfx and' agganciT :for positive 'cos fscribed in oscillationsV Willfs'tp.

ffice' usefull to provide a "monitor, or -f"memory lthe. power `level `Voi.' 'the oscillator` l 36 or `55v mally Eisfoifsuch A x3. yThe impedance (element then re "sive,Y onnn-oscillatng.

-tutigaat,serene. A '0,'if fitinttaas'ea bevanda-2,

This eriafateristic'tfthe pgseatdevice `may Y of ther source 'connected injits 'p1`afce. Thusl @suppose ,the device` is connected'jinaeystem where nor- Vaivameth'at 'rfjis ess than t HSDS- s Y KLShouldlEir'icrease' rito above vj:t' 3,;` for' any vreason, "'the""'variable ivi-impedance f device "Will start "oscillating and 'iwill f'rmain oscillating. Its oscilla-'tion is f therefore 'an indication" thatEis 'increased Tali e the V"critical"value, The sustained character" iithe after of the previous increase in' E,'ev`e though ,fr that increase may have beenonl'yrmomentary. AIn thisway the device remembers theprevi'ous parallel resonant circuit formed by capacitance C and inductance L connected across source '36. The losses in the resonator are represented by the shunt resistor Rr. Connected in parallel with the resonator 2| is the impedance Zr. of load 31. The parallel connection of Rr and ZL produces a resultant impedance R', in the notation used above.

As shown above, the effect of turning on the electron stream in the apparatus is the same as connecting an impedance Zb in parallel with the resonator -2|. This alternating current beam impedance may be considered as parallel-connected resistance Rb and reactance Xb, given by Equations 6 and 7 above.

By virtue of the conjunction of the resonator 2l or 2l with the variable impedance element provided by the electron-discharge portion of the apparatus, further uses are possible in addition to those discussed above. Y In normal operation, a cavity resonator, such as 2| or 2|',

has a definite resonant frequency and a definite meritfactor Q (usually defined as the ratio of stored energy to energy dissipated per cycle). The device of the present invention illustrated in Figs. 20 and 2l permits accurate and easy control of either or both of these factors.

It-will be appreciated that the effective reactance Xb exhibited by the electron stream is connected in shunt with the resonator, as shown in Fig. 26. Accordingly, the resultant resonant Y frequency of the entire device including the g duced by varying En) for a fixed value of input voltage E and fixed Eo and EG. Accordingly, this apparatus can be. utilized, for example, wherever a variably tuned cavityresonator is required.

In addition to permitting variable tuningover a wide range of resonant frequencies, the Q of the resonator, which is a measure of selectivity, can also be independently controlled. One such use for such a device would be in a multichannel receiver. Here the resonant frequency. of, the cavity resonator (which might be coupled directly to a receiving antenna serving Yas the source 36 of the previous figures) can be shifted in tuning from one channel to another merely by changing the operating voltages, preferably EG and/ or Ea. Thus, a simple switch might be provided changing the voltage En in steps, each position of the switch then corresponding A-to a single channel. Alternatively, the tuningof the resonator device may be effected in response to the frequency of the incoming wave, by a suitable automatic frequency control circuit, so 'as to maintain the tuned circuit 2| or 2l in resonance with the incoming frequency. At the same time the selectivity can be independently controlled. As shown in Fig. 28, a wide range of Q, and hence of selectivity control, can be obtained. In addition, byproper adjustment of Io to a value which completely prevents any o-scillations whatever (that is, to a value below the starting'current necessary for a reflexoscillator) Vthe Q can be made theoretically infinite when'operating with input voltages producing a value of r in the neighborhood of 3.83, as shown in Fig. 6.

The present invention also provides apparatus automatically variable in Q as the signal level changes. For example, when the signal level decreases, it is advantageous to increase the Q in order to discriminate more strongly against noise voltages, and When the signal level is high, lower Q and broader selectivity may be desirable.

These features may be obtained, according to the present invention, by adjusting the operating point of the variable impedance element of Fig. 20 or 21 to a condition such as at c in Fig. 6. For this condition, an increase in E produces an increase in r which causes a decrease in the magnitude of the negative resistance and hence a decrease in Q. Conversely, a decrease in E produces an increase in Q.

It is also possible to vary the resonant frequency substantially without change in Q, that is, to produce a variable frequency constant Q circuit, which is highly advantageous in filter Work. This is illustrated in Fig. 29, which shows an admittance plot in which the ordinate axis represents susceptance Bb of the beam and the abscissa axis represents beam conductance G1. As indicated above relative to- Fig. 5, for a constant value of Io and variable the admittance values of the beam have a locus along a circle with the center at the origin. Such a circle is shown at c in Fig. 29. To produce variable resonant frequency for a resonator incorporating the present variable impedance element, it is necessary for the susceptance Bb to vary over a Wide range. Accordingly, for variable-frequency constant-Q operation, the admittance Yb of the electron beam should vary along the line li. This can be readily obtained according to the present invention. As noted above, for a change in gb, both Bb and Gb change. By simultaneously adjusting In by control of EG, the value of G11 can be kept substantially constant while Bb varies widely, thereby producing the locus Z1 as desired. This, of course, requires simultaneous control of both EG and Ea in non-linear fashion. Such control can be obtained in conventionalrnanner by suitably designed non-linear gangedV voltage dividers or by suitably designed ganged cams operating linear voltage dividers, such as in the voltage sources 3l and 32.

Another type of operation possible with the present device is as a constant-frequency variable-selectivity tuned circuit. Such a circuit is almost impossible of attainment at ordinary frequencies or with ordinary devices, but is readily provided by the present invention. As illustrated also in Fig. 29, for constant frequency operation, the susceptance Bb of the beam must be maintained constant While the conductance Gb ,varies to produce variable Q. Accordingly,jthe locus of beam admittance points must be the line lz of Fig. 29. This is also produced in the same manner discussed above with respect to the locus Z1, by ganging theER and EG controls, but in an obviously dilerent manner.

However, in this connection, certain restrictions on the range of Variation are imposed by the fact that self-sustained oscillations must be prevented. As noted above, if the combined positive conductance of the resonator and its external circuit is less in magnitude than the negative conductance of the electron beam, selfsustained oscillations are produced. 'I'his provides a limit in one direction for the variation in G and hence for the variation in Q. As the value oflhGdapproaches the yaliie "at which oscillations Woduid fb" pr/"d'llcedffth bcCitieslflilgyh'ir and since the losses'y 'nsiwdidbreek 'dus thee-etai eenduerenee V and Qis theoretically"'iniiiiite "npra'cf ne efcourse;wmiefvefy'nigh veneeof Q are dba tainalolef the oscillation point inust be avoided. frnjie'iedpnejby keeping're below the-'starting cui: rsh?. Velliihs. Dntty r useffor tli'edeyice of the present inveel; n of; Z'l'is asa feedback control:` for a regenerative' damuatrj. Aaegiampie-fsuch "oscillator 'is ehdwrr in11rigj-'3o, endeemprisee einen; fdavity' eter-e1 qi. and l uz ,joined by drift rubens;

2.75, granted-Maico; 194.1,sueh e 'device' operates asf-a veideity-inoddianen"ernennen known as' "e e oseillationsare produced. A'eedback pfath 1s'11lustrated 'atin Fig. 30 and has inserted in 'avariepieimpedance; element 2 5, eden as so. el such a variable impedance discussed aloovv v y ele'rne '1;can` .e 'used' asf a' phase-'shift 'device-or line-stretcherf'and thus 'can change the" fre` quency of oscillation of theoscillator device. By con Iolli'n'g; this'fphase shift by 'modulating sign sfifrornj source V543, Yfrequency 'inodiilatim is pY uc dg' "Alternatively "or, A"additionally, the

A i illation can be'adju's'ted by ad'- iden-11g; theempntude er une'` feedback by uns variable .impedance varied inaccordance with modulatine si l 'amplitude modulation of rthe outputis' d ,1i/ed-` Iithis way an eXtremelY vertilfedcontrol useful for'va'djustment or modulation idea-v Y p "S any changes could be made in the ab vaconstructionj and manyapparently widely` d -'nte bodiments'othis invention couldfl'oe amplitude eff es without departingffrr'n the. Scope; thereof! inteindenv that. al1v matter contained in the n ,i arebemg'dir'eeuy reduced negative G; "At"midpointiatfvvhicu de#A uiustrated ifi any of Figs. '7, 8, 85519', 20.

h the interior 'er' drift' tube durend. eend eapaem resonator' l o2; andre` element 25. If such adjust# accelerating velectrons from said cathode through to said'walls.' acathodeoppos'iteone of said elec#4 sa'd. 'cath e5 e' destinarn; 0r, shown in. the. annoncen. iI drawings shall loe, interpreted as illustrative amino alimitine sense..

what'. isclaimed iS:

1;A variable. impedance element comprising e uency-energy "conductor, va pair? of .permeable velectrodes. coupled. GO Seid, or 'and detningy a gaplacross which a e impressedrbyjsaid. corlclilfctoi'y a cathode d with vsaid electrodes on one side thereof .eector'electrode aligned with Said. eleco one side thereof,z oppsitefsaid cathode.,

9e @pple between. saidj dethede. and, one of said. ele and, Va source "of, electron-reflectingr v e'"coupled betweensaid cathode" andfsfaid reflector eletode, saidjpotenuals.having aimee.-

tude adapted 'to produce/a passive non-'os'cilf leterrcondtmn fOrSad element.'

fehle impedance. element adapted. for use at ultra-high frequencies','comprising. an ultra-high-ftrequency input conductor adapted. to

befcoupled to a" source of vultralhigh frequency adapted tb De mp1s@ i0. a 1.1i.

source.. ""of: "eiectronacceleratine' potential tion device f0.1?.

source Aof electron-reine ultra-highfrequency energy, and a passive nono'scillatorf electron-discharge device coupled to saidf-conductorsfbetween said source and utilization" device." said discharge` device comprising' a pair" of electron-permeable electrodes coupled to" both saidc'onductors, a cathode aligned with said electrode's'on Oneside' thereof, and a reflectorVv electrode v"aligned With said cathode and electrodes 'on the otherfside of said electrodes, po'-v tential supply means coupled to said cathode for saidffelectrodes',` and potential supply means coupledl vto 'said reiie'cftor electrode for' returning saidelectrontl'irough said electrodes while "pre' ventin'generationof oscillationsby said elec'- tronsb'etweeri'saidelectrodes. 'f'

variable` impedance" element for ultrahigh-freduericy venergy comprising a hollow coniductivew'ave uidehaving 'a pair of `opposite walls, a' pair'oi electron permeable-electrodes connected' trodeslY` a' reector"'electrode opposite another of said'electro'desja ysource of 'electron-accelerating potential`-copleclf between said cathode and onej of `A said y"elect'ro'n-perrriealcle electrodes, and Aa lling' potential coupled between said cathode andsaid'reflector electrode, saidpotntials being proportionedto produce a nonoscillator'y condition between said electron permealcle electrodes.V

4. Apparatus" as in said electrodes' isl coupled vto its wave guide wall` byfmeans' of" al cylindrical' conductive in emlcerv extendinginwardlyV from thewall of said'gui'de `5,""Ai` variable impedance device for ultra-highfrequency energy'V comprisingfa coaxial Vtransmis'- sioilineiha'ving an inner 'conductor and an'outer conduotorg'apair 'of electron-permeable electrodes co fpledl respectively to "said conductors, a cathode oppositeone of said electrodes, a reflector elecj, "aligned 'with""said cathode and electrodes' o nj" efotlie'r sideof said electrodes, v"a source'of electron-*ac elerating potential coupled between ede"a`nd one of said electron-permeable elec o des; and'afsourceoi electron-repelling pov` tential' coupled between sad cathode yand'said reflector"electrode,4 said potentials being' proportionedto produce a non-oscillatory condition betweensaid vele' ctronperrneable electrodes;

` 'f as irrelaiimS, wherein said transmission lf forms' an input connectionfand f urtherjincluding a second coaxial transmission line havingjaniinner conductor and an outerv con` ducto'rco 'ecte'd'respectively to vsaid electrodes andfconstitutrie an. output Connection! '7. A variablefimpedance device for ultra-highfrequencies` comprising an input ultra-high-frequencyen ergxff` conductor, an output ultra-highfrequency' energy conductor. a cavityv resonator to said" cathode fon accelerating coupled Yto liothV said conductors and having a pairv of adjacent electron-permeable walls, a cath ode/opposite'ojne of said walls, a reflectorelectrode opposite the other ofsaid walls, means coupled the electrons therefrfrornto, pass through said walls, 'and "a sofurceof 'potential coupled to said reflector elec` trodef for causing` the said electrons'to re-enter said resonator while preventing the *generation of. self-sustained oscillations therein.

The method of producing va variable passive impedanceuseful at ultra-high frequencies, com# pfrising' the stepsjof producing a stream of electrdr'islsuljjectifng said electrons tothe actionfof claim 3, wherein one 'of 

